The present invention is an apparatus and method to confine contaminated particulate matter contaminated with an organic compound and to aerobically biodegrade the organic contaminant. In particular, the invention is an apparatus and a process utilizing the apparatus to confine soil contaminated with a hydrocarbon formulation, such as gasoline, diesel oil and the like, and to biodegrade the hydrocarbon.
Contamination of soils and groundwater with petroleum products has become one of the major threats to groundwater quality in the United States. A lack of control historically on siting storage tanks coupled with a high rate of tank system failure and the toxic properties of gasoline has created a critical problem for both public and private sectors. Most spill recovery systems available for organic compounds do not address the removal of residual levels of the compounds in the soil, which normally make up an estimated 40 percent to 100 percent of the spilled fluid. Although petroleum products are nominally considered to be hydrocarbons the spilled organic compounds may include detergents, soaps, phosphate esters, methanol, ethanol, ethylene glycol and other additives.
A particular problem facing the retail gasoline industry is the treatment and disposal of spoil piles generated during tank replacement operations. These spoils, typically, are lightly to moderately contaminated soils resulting from spillage, overfilling, and small line leaks in the tank pit. Several hundred cubic yards of soil are commonly removed during tank replacement.
Because of the relatively low level of contamination, often less than 200 ppm, these soils, while in the tank pit, do not represent a significant or immediate hazard to the environment, and, therefore, require no treatment if left in place. However, once excavated, these low levels of contamination require that the soil be treated or removed for disposal. Disposal at secure landfills in 1986 cost $100,000-150,000 per site or more. A low-cost, effective method of on site treatment would offer considerable savings to the industry while providing protection for the environment.
U.S. Pat. No. 3,616,204 to Linn discloses that many species of yeast, bacteria and molds consume hydrocarbons and their derivatives, such as sulfurcontaining organic compounds. Some species are rather specific, even to the molecular weight range. Most of these microorganisms are aerobic, that is, they require molecular oxygen in addition to the carbon from the organic compounds. Further, most require a nutrient medium containing various mineral salts and, depending on the species, ph within a controlled range.
The patent of Linn teaches a process to reduce the contamination of a soil containing organic compounds, such as hydrocarbons and the like, by harrowing or plowing, to increase the permeability of the soil, inoculating the soil with a microorganism capable of metabolizing the organic compound, contacting the soil with a nutrient for the microorganism, and maintaining a gaseous environment such as air adjacent to the soil.
However, the process of the patent to Linn is not suitable for treating soils which must be removed to replace a leaking tank, as most gasoline tanks are not located in the rural farm areas but in areas with considerable paving which results in a high run-off which would tend to spread the contamination to groundwater and aquifers.
It is well-known that indigenous microorganisms in the soil are able to mineralize not only hydrocarbons but most organic compounds. Alexander, M., "Biodegradation of Chemicals of Environmental Concern," Science, Vol. 211,9, January 1981 at pages 132 to 138 discloses that the microorganisms may adapt to utilize the contaminating organic compound as a sole source of organic carbon, or may cometabilize the contaminating compound, that is utilize the contaminating compound together with their normal substrate. As petroleum hydrocarbons generally constitute the largest fraction of the spilled organic compound, the hydrocarbon degrading microorganisms provide a reliable index of the useful microorganisms in the soil.
U.S. Pat. No. 3,846,290 to Raymond discloses a process for utilizing indigenous microorganisms to biodegrade hydrocarbons in contaminated groundwaters. The patent teaches that the hydrocarbons can be completely mineralized by adding nutrients to the groundwater and maintaining the groundwater aerobic.
However, U.S. Pat. No. 3,846,290 relies upon the flow of the groundwater to transfer both the nutrients and the oxygen to the microorganisms. Therefore, the process would not be suitable for biodegrading contaminated particulate matter such as soils which are not in proximity to groundwater.